1. Field of the Invention
The present invention relates to an optical lens assembly for image taking, and more particularly to an optical lens assembly that provides a wide-angle view by four lens elements and the optical lens assembly can be applied to infrared band of electronic products.
2. Description of the Related Art
In recent years, vehicle mount cameras or surveillance cameras have an increasingly demand, and the vehicle mount cameras are generally used for photographing omnimax road conditions or recording a scene before or after a motor vehicle, and the main requirements include a wide angle and a capability of recording images of infrared bands, such that images with a larger width or from a dark environment can be captured by an optical lens. Other applications such as surveillance systems of roads or buildings also require an optical lens with a greater field angle and a capability of taking images formed by light of regular band and/or infrared band. In popular interactive electronic games, a near-infrared image taking method is generally used for detecting a current motion of players to achieve an interactive entertainment effect between the players and the games, and thus there is an urgent need for an optical lens capable of taking an image within the infrared band.
Many different designs are available for the optical lens assembly having a wide-angle optical lens with a fixed focal length. As science and technology advance, the development of electronic products such as digital cameras, web cameras and mobile phone cameras tends to have a compact design to meet the user requirements for an optical lens assembly with the features of low cost, good aberration correction ability, high resolution, and high image quality.
In general, conventional wide-angle optical lens assemblies come with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. As disclosed in U.S. Pat. Publication Nos. 2009/080089, 2010/157443, and 2010/231686, a 3-lens design was adopted; as disclosed in European Pat. No. 2056151, a 4-lens design was adopted, and as disclosed in WIPO Pat. Publication No. 2010007845 and U.S. Pat. No. 7,768,719, a 5-lens design was adopted. If the image quality is taken into consideration, the optical lens assemblies with the four-lens and five-lens designs have advantages on aberration correction and distortion correction caused by the wide angle, and the four-lens design contains less lenses than the five-lens design, and thus incurring a lower cost, so that the 4-lens design can be adopted in the wide-angle optical lens having a good image quality.
In various designs of the four-lens optical lens assembly having a greater field angle, the prior art adopts different combination of positive and/or negative refractive powers, wherein a design having the first lens element with negative refractive power, the second lens element with positive refractive power, the third lens element with positive refractive power, and the fourth lens element with negative refractive power was disclosed in U.S. Pat. No. 6,043,941; a design having the first lens element with positive refractive power, the second lens element with negative refractive power, the third lens element with positive refractive power, and the fourth lens element with positive refractive power was disclosed in U.S. Pat. Publication No. 2003/161054; and a design having the first lens element with negative refractive power, the second lens element with negative refractive power, the third lens element with positive refractive power and the fourth lens element with positive refractive power was disclosed in European Pat. No. 2009476.
In the design with a greater field angle, a greater image aberration occurs at off-axis and close to edges of an image. To achieve the requirement for a high quality of the optical lens assembly, a better design should be provided for compensating the image aberration. To use in small optical lenses, the increasing of the field angle is not to sacrifice the optical effective radius. To meet the all-weather image taking requirement, the optical lens assembly should still provide a good aberration correction for images within the infrared band. Therefore, the present invention provides a practical and feasible design that uses a combination of different refractive indexes, concave optical sides and convex optical sides of the four lenses to enhance the field angle, and provides a good aberration correction within visible and infrared bands, so that the optical lens assembly can be applied to infrared image taking optical lens of electronic products and interactive electronic games.